Hooded crossover tube



April 18, 1961 L. A. WARD HOODED CROSSOVER TUBE Filed April 25, 1958IN/VENTOR LESLIE A WARD HOODED CROSSOVER TUBE Leslie A. Ward, WestHartford, Conn., assignor to United Aircraft Corporation, East Hartford,Conn., a corporation of Delaware Filed Apr. 25, 1958, Ser. No. 730,914

1 Claim. (Cl. 6039.66)

It is a further object of this invention to teach combustion chamberconstruction which provides a convergent cooling gas passage immediatelydownstream of crossover tubes to direct external cooling fluidfsuch asair, in close proximity to the combustion chamber external surfaceimmediately downstream of the crossover tube and then into thecombustion chamber for combustion chamber wall internal'surface coolingpurposes.

Other objects and advantages will be apparent from the specification andclaim, and from the accompanying drawings which illustrate an embodimentof the invention.

Fig. 1 is a front view of a plurality of combustion chambers containedwithin a burner unit outer housing and connected internally by crossovertubes.

Fig. 2 is a showing along line 2 2 of Fig. 1.

Fig. 3 is a showing along line 3-3 of Fig. 2.

It is common practice in powerplants' of the type used in modernaircraft engines and fully disclosed in US. Patent Nos. 2,711,631 and2,747,367 to utilize a plurality of combustion chambers, each of whichdefines a combustion zone. For the purpose of initial ignition andcontinuous combustion, it has become customary to join the interiors ofadjacent combustion chambers through a passage defined by telescopinghollow tubes, called crossover tubes, so that when ignition occurs inone of the combustion chambers, a burning fuel-air mixture will passthrough the crossover tubes to ignite the fuel-air mixture in theadjacent combustion chamber. As the combustion chambers and crossovertubes operate at elevated temperatures due to their proximity to theactual combustion process, it has been necessary to pass a cooling fluidsuch as compressor air over the combustion chamber and even into thecombustion chambers in a fashion to be described hereinafter to cool thecombustion chamber shell. Experience has shown that substantialcombustion chamber shell destruction has occurred immediately downstreamof the combustion chamber shell-to-crossover tube connection and alongthe downstream surface of the crossover tubes, due to the relativelystagnant cooling fluid flow region established there by the coolingfluid passing over the crossover tube. It is a purpose of this inventionto efficiently provide cooling-fluid to this region of the combustionchamber shell immediately downstream of the crossover tube and along thecrossover tube downstream surface.

Referring to Fig. 1 we see burner unit 10 which com- 2,979,898 PatentedApr. 18, 1961 prises burner'outer case 12, which is of circular crosssection about axis 14 and which cooperate with a compressor case andturbine case to define an engine outer case which envelops axiallyaligned compressor, burner and turbine units in the fashion described inUS. Patent Nos.- 2,711,631 and 2,747,367. Burner unit 10 may be of anyconventional type, for example, of the type shown in U .S. Patent Nos.2,674,090 and 2,676,460. Burner outer case 12 envelops a plurality ofcombustion chambers 16, which constitute enveloping shells forcombustion zones. While not necessarily so limited, combustion.

through the cavities 22 of Fig. 1 soas to communicate with the hollowinterior of combustion chamber 16 and further to coact with the fuelmanifold construction which provides fuel thereto in supportingcombustion chambers 16 preferably in the fashion taught in US. PatentNo. 2,686,401. A swirler vane ring 24 engages and surrounds fuel nozzle20 and serves to introduce swirling air to the interior of combustionchamber 16 to mix with the atomized fuel from fuel nozzle 20 and providea combustible fuel-air mixture within combustion chamber 16. Anyconvenient ignition means such as spark plug 26 or an explosive chargemay be used to ignite the fuel-air mixture within combustion chamberchamber 16. Combustion air is provided intotheinterior ofcombustionchamber 16 through combustion air entry holes 28 while combustionchamber cooling air is passed axially along the exterior of combustionchamber outer wall or shell 18 as well as alongthe interior surface ofat least a portion of shell 18 through apertures 30 and 32, whichapertures are positioned to extend substantially axially to interceptcooling air flow. The cooling air, combustion air and swirler airmentioned supra are pref:

erably provided from the engine compressor which is located immediatelyupstream of burner unit 10. While not necessarily so limited, combustionchamber 16 may have a center tube 34 which extends from the combustionchamber forward end 36 rearwardly or downstream axially for at least aportion of the axial dimension of combustion chamber 16.

Crossover tube units 40, which preferably comprise telescoping hollowmetal tubes 42 and 44 extend between adjacent combustion chambers 16 andserve to place the combustion chamber interiors in communication forpurposes of initial ignition and re-ignition as described supra. Thehollow tubes of crossover tube unit 40 may be attached to combustionchamber shell 18 by any convenient method such as the weldment of ringflange 46 to tubes 42 and 44 and to shells 18.

As mentioned supra, cooling fluid passes through burner unit 10 andaround, preferably axially, combustion chamber shell 18 to serve to coolthe exterior surface of the combustion chamber shell 18 and also to passthrough forwardly opening apertures 30 and 32 and thence along the innersurface of combustion chamber shell 18 to provide additional coolingthereto. The cooling air flow is indicated by arrows in Figs. 2 and 3and it will be apparent that, due to the substantially axial directionof flow, a stagnant region or poor circulation zone will be formedadjacent shell 18 immediately downstream or aft of crossover tube units40, thereby causing local overheating and eventual destruction ofcombustion chamber shell 18 in this vicinity.

Applicant proposes to utilize crossover tube hoods 50 to be positionedimmediately downstream of crossover tube unit 40 and extend downstreamimmediately beyond apertures 32 and to be spaced slightly outwardly ofburner shell 18 a distance substantially less than the distance betweentube unit 40 and apertures 3'2'and extend laterally and symmetrically oneach side of crossover tube unit 40 at the hood forward end 52 to definea cooling air inlet port 51 in the form of 'a continuous slot and toattach to burner shell 18, by any convenient means such as weldin'g, atits downstream end '54, and at side surfaces56 and 58 such that hood 50forms a shallow cooling air passage 53 between inlet port 51 andapertures 32. Since hood 50 is symmetric with respect to crossover tubeunit 40 and is of convergent shape, that is, its upstream end 52 issubstan tially larger than its downstreamend 54, the cooling gas passage53 formed between hood 50 and burner shell 18 will be convergent andshallow so that the cooling air will be forced to flow at rapid velocitythrough the region immediately downstream of crossover tube units 40 andoverthedownstream surface of units 40 and thence into the interior ofcombustion chamber 16 through apertures 32. In this fashion, combustionchamber burner shell 18 is cooled by cooling air flow immediatelydownstream of crossover tube unit 40. It will be noted that hood 50partially encircles tubes 42 and 44 due to its fragmentary circularsection 57 at inlet or upstream end 52.

Preferably, crossover tube unit 40, combustion chamber 1'6,fuel nozzle20, swirler unit 24 and center tube 34 are of circular cross section,with all but unit 40 having parallel axes to axis 14.

It is to be understood that the invention is not limited to the specificembodiment herein illustrated and described but may be used in otherways without departure from its spirit as defined by the followingclaim.

I claim:

In abiirn'er unit, "a'cornbustion z'one enveloping s'he'et metal shell,means to pass cooling fluid over the outer periphery of said shell toestablish a direction of cooling fluid flow, a substantially cylindricalhollow tube having a downstream surface and projecting externally fromthe outer'periphery of said shell and communicating with said combustionzone, at least one aperture extending through said shell and located arelatively short distance downstream of said tube in alignment therewithin said direction of cooling fluid fiow therefrom, and a solid sheetmetal hood having a periphery including a forward end which has a widthsubstantially greater than said distance between said tube and saidaperture and which also has a centrally located, substantallysemi-circular recess therein and with the remainder of said forward endextending symmetrically beyond said recess and the remainder of saidperiphery including an after end which is narrower than said forward endand two sides converging from said forward tosaid after-end, means toattach said remainder of said hood periphery to the exterior of saidshell and with said hood spaced in relation thereto a distancesubstantially less than said distance between said tube and saidaperture symmetrically so that said recess encircles the downstreamsurface of said cylindrical tube while said remainder of said hoodforward end extends symmetrically and laterally on opposite sides ofsaid tube to define a continuous inlet slot with said shell and so thatthe remainder of said hood periphery is in sealing engagement.

with said shell exterior with said hood after end extending immediatelybeyond said aperture so that said hood defines a shallow cooling airpassage with said said shell exterior having a continuous slot inletsymmetric about and extending laterally on each side of said'tube andwhich then converges symmetrically from said inlet to said aperture sothat'the cooling air intercepted by said inlet is causedto pass at highvelocity over the downstream surface of said hollow tube and said shellouter periphery immediately adjacent said hollow tube and then throughsaid aperture in'to'said shell.

References Cited in the file of this patent UNITED STATES PATENTS2,541,171 McGarry Feb. 13, 1951 2,679,136 Qaubatz May 25,1954; 2,722,803Travers Nov. 8, 1955 2,851,859 Four Sept. 16, 1958 FOREIGN PATENTS545,787 Canada Sept. 3, 1957 (Corresponding Belgian Patent 516,800, Jan.31, 1953.) 516,800 Belgium Jan. 31, 1953- 6l9,251 Great Britain Mar. 7,1949 yd I

